WASHINGTON (CNN) -- When President Obama gave a Medal of Honor to Sgt. 1st Class Jared Monti's family this week, it was just the sixth time the nation's highest medal for valor has been awarded to a hero of the current conflicts.

Sgt. 1st Class Jared Monti is one of six Medal of Honor recipients -- all awarded posthumously -- in current wars.

In all six cases, the awards were presented posthumously.

During World War II, the D-Day invasion of Normandy produced four recipients, the attack on Pearl Harbor produced 15, and the battle of Iwo Jima had 27.

In all, more than 3,400 Medals of Honor have been awarded since the medal was created during the Civil War, with about 620 of them bestowed posthumously.

Why then have there been so few recipients -- and only deceased ones -- for Iraq and Afghanistan?

Littrell is one of 95 living Medal of Honor recipients in the United States. More than 50 of them gathered this week in Chicago, Illinois, for their annual convention. Each year, the gathering gets smaller.

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The decrease in the number of Medals of Honor is not a result of any change in the criteria for the award.

"The rules haven't changed; the rules and the requirements are still the same," said Gen. James Conway, commandant of the U.S. Marine Corps.

The honor is given to service members who distinguish themselves "conspicuously by gallantry and intrepidity at the risk of his life above and beyond the call of duty while engaged in an action against an enemy of the United States."

The phrase "at the risk of his life" may help explain why since World War II most medals have been awarded posthumously.

"I think it has something to do with the level of intensity of the conflict," Conway said. "If you go back and look at some of the fights that took place in Vietnam, Korea, World War II, there were massive numbers of troops involved in massive engagements over a period of days. That's not the type of conflict that we are seeing in a type of counterinsurgency in Iraq and Afghanistan.

"So I think that's perhaps the single most determining factor here as you look at awarding or not awarding a medal."

In many respects, no one wants any more Medals of Honor awarded.

"You don't want your soldiers to be put in that situation to where any of them have to rise to the occasion," said Brian Thacker, an Army veteran who earned the Medal of Honor in Vietnam.

Conway echoed that sentiment. "Any time a soldier or a Marine wins the medal, then his unit is in extremis, and he's doing very heroic things ... to make that situation better. I don't want to wish that on anybody."

But the United States has nearly 200,000 troops fighting two wars, and that means troops risking their lives, displaying gallantry. And even at the highest levels, people want those heroes recognized, especially if the honoree can be there for a ceremony at the White House.

"This has been a source of real concern to me," Defense Secretary Robert Gates said.

"I think it was one of President Bush's real regrets that he did not have the opportunity to honor a living Medal of Honor recipient," added Gates, who also was defense chief in the final two years of Bush's administration.

Thacker is optimistic the day will come.

"There are going to be many opportunities as this conflict goes on," he said. As the critical situations come up, "there is no question that the men and women will rise to the occasion. It's just a matter of whether or not they get documented -- whether all the pieces fall into place to get a living recipient."